It is generally preferable that a truck or other large-sized delivery vehicle traveling on unpaved rough roads more often than an ordinary passenger car has an engine which takes in not air near the ground containing plenty of dust but clean air at a sufficient height above the ground. Further, for fear of splashing rainwater or snow near the ground being taken in together, it is preferable to ensure that the engine takes in only the air at the sufficient height above the ground.
To these ends, as exemplarily shown in FIG. 1, mounted on a rear of a cab a in the large-sized delivery vehicle is an air intake duct b which extends vertically. This kind of air intake duct b comprises a duct body d as an outer shell with an air intake c opened on an upper portion of the duct body to take in ambient air as intake air for an engine, and a louver e which covers the air intake c to prevent intrusion of matter other than the ambient air.
In the air intake duct b, the air intake c is opened wide backward of the vehicle and, as shown, may be opened also on a laterally outer right side of the vehicle. With such structure having the air intake c opened on the adjacent two sides, even if a hood for a cargo bed covers and conceals a rear of the air intake duct b, the air intake c can be prevented from being completely concealed. Thus, the engine can be prevented beforehand from being accidentally fired due to failed intake of the ambient air.
There exists, for example, below-mentioned Patent Literature 1 showing state-of-art technology pertinent to this kind of air intake duct.